The biggest problem with Vista is the UAC, and as its new protection scheme to prevent things from being written to the Program Files directory.

There are many things you can try and a quick search of this forum will turn up many additional things you can try.

One set Poser to run in administrative mode
Two you can try turning off the UAC (Open up Control Panel, and type in "UAC" into the search box. You'll see a link for "Turn User Account Control (UAC) on or off")

Just do a quick search on this forum and vista to see the other recommendations.  

Shawn McCarthy
www.defyallchallenges.com